Double wall combustion chamber

ABSTRACT

A combustion chamber for a gas turbine power plant of the stepliner type including a plurality of annular double wall stepliner portions. The portions are of various sizes and are arranged concentrically and in order of increasing size from the upstream end toward the downstream end of the chamber. Each double wall liner portion includes an alternating smooth wall member and a serpentinous wall member. In one step, the smooth wall member is the radially inner wall and an overlapping portion of the serpentinous wall member is the radially outer wall. In the adjacent larger step, the serpentinous wall member is the radially inner wall and an overlapping portion of a larger diameter smooth wall member is the radially outer wall. The effect of this construction is to provide a combustion chamber capable of withstanding higher burning temperatures.

United States Patent De Corso et al.

[451 Nov. 7, 1972 [72] Inventors: Serafino M. De Corso, Media; Carl W.Carlson, Holmes, both of Pa.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

22] Filed: Jan. 13,1971

211 Appl.No.: 106,041

[52] US. Cl. ..60/39.65, 60/3931, 60/3937, 1 60/3966 [51] Int. Cl ..F02g3/00 [58] Field of Search....60/39.65, 39.66, 39.32, 39.31, 60/3937;431/352 [56] References Cited UNITED STATES PATENTS 2,610,467 9/1952Miller ..60/39.65 3,169,367 2/1965 I-Iussey ..60/39.65 3,545,202 12/1970Batt ..60/39.65

FOREIGN PATENTS OR APPLICATIONS 229,934 2/1944 Switzerland ..60/ 39.65

Great Britain ..60/39.65 Great Britain ..60/ 39.65

Primary Examiner-Douglas I-lart Att0rneyA. T. Stratton, F. P. Lyle andF. Cristiano, Jr.

[5 7] ABSTRACT A combustion chamber for a gas turbine power plant of thestep-liner type including a plurality of annular double wall step-linerportions. The portions are of various sizes and are arrangedconcentrically and in order of increasing size from the upstream endtoward the downstream end of the chamber. .Each double wall linerportion includes an alternating smooth wall member and a serpentinouswall member. In one step, the smooth wall member is the radially innerwall and an overlapping portion of the serpentinous wall member is theradially outer wall. In the adjacent larger step, the serpentinous wallmember is the radially inner wall and an overlapping portion of a largerdiameter smooth wall member is the radially outer wall. The effect ofthis construction is to provide a combustion chamber capable ofwithstanding higher burning temperatures.

20 Claims, 4 Drawing Figures PATENTEDnnv 1 I972 SHEET 1 BF 2 IIINVENTORS Serofino M. DeCorso Cori W Carlson WITNESSES PATENTED 7 SHEEI2 OF 2 N V CE vm mm mm mm mm BACKGROUND OF THE INVENTION One seriousproblem in gas turbine power plants is reliable combustion chambers orcombustors, capable of withstanding high temperatures for extended oftime. I v

Historically, a substantial step forward was taken when the step-linertype combustion chamber having corrugated spacer members betweenadjacent liners was disclosed by E. F. Miller, US. Pat. No. 2,610,467,issued on Sept. 16, 1952, and assigned to the present assignee. In thisnow'well known construction, cooling air is admitted from the plenumchamber through axially extending spaces in the corrugated members, toprovide a flow of relatively cool air to insulate the inner surface ofthe combustion chamber wall from the hot combustion gases. Otherimprovements on this construction are disclosed in the followingpatents: S. Way, U.S. Pat. NO. 2,448,561 patented on Sept. 7, 1948; W.L. Christensen, U.S. Pat. No. 2,537,033, patented Jan. 9, 1951; R. A.Sforzine, US. Pat. No. 2,549,858, patented Apr. 24, 1951; and E. A.DeZubay et al., U.S. Pat. No. 2,573,694, patented Nov. 6, 1951, all ofthe preceding patents being assigned to the present assignee.

Of course, the higher the temperature of the combustion chamber wallsduring normal operation, the more subject the chambers are to thermalstress and strain. This requires constant maintenance programs wherebycombustion chambers must be periodically inspected to ensure theiroperating reliabilities. More recently, because of the advent of largergas turbine power plants, it has become desirable to operate the plantsat higher and higher temperatures. Furthermore, because of the economyinvolved, it is more desirable to burn heavy residual fuels, which arehigh in contaminants, rather than the purer fuels, such as No. 2distillate fuel. However, residual fuels radiate substantially more heatto the combustor walls, so that combustor life and reliability issubstantially reduced.

One such solution to enable combustion chambers to operate at highertemperatures is the refractory or ceramic combustion chamber. But as ofnow, thehigh velocities and violent pulsations in the combustionchambers have prevented the use of refractories in combustors incommercial applications.

Another such solution is to introduce more cooling air to the combustorwalls. However, this decreases the overall efficiency of the turbine andhas an adverse effect on the temperature distribution pattern of thegases when it is introduced to the turbine blades since there is a largetemperature differential between the blade tips where the cooler air isand the blade centers causing serious thermal stress and strain.

It would be desirable, then, to design a combustion chamber which wouldoperate at higher temperatures for extended periods of time, or in thealternative operate at cooler temperatures than present combustorsoperating at normal conditions, so that it would be subjected to fewerthermal stress and strains than present combustors. This in turn wouldrequire less periodic inspections since its reliability would besubstantially increased. It would further be desirable to design acombustor that would be economical to construct and easy to assemble.

SUMMARY OF THE INVENTION The following disclosure relates to acombustion chamber structure for a gas turbine and more particularly toan improved apparatus of this type.

gas turbine power plant has a compressor section, in which is disposedat least one combustor or combustion chamber, and a turbine section. Thecombustion chamber is of the step-liner type and is comprised of aplurality of double wall portions. The double wall portions are ofstepped configuration, each of the portions being of greater diameterthan the preceding portion frorn'the upstream to the downstream end ofthe combustor. Each liner portion includes altemating smooth wall memberand a serpentinous or corrusated Wa membe In one step or portion, theaxially extending smooth wall forms the radially inner wall and apartially telescoping or overlapping serpentinous wall member forms theradially outer wall. One part of the serpentinous member overlapsapproximately half of the smaller diameter smooth member andapproximately one-half of the serpentinous member extends in adownstream axial direction. A second larger diameter smooth wall member,in turn overlaps the extending half of the adjacent serpentinous member,to cooperatively form a second double wall portion.

The adjacent ends of the alternating smooth members .of the wallportions are approximately aligned in a radial direction relative to theaxial centerline of the combustor. The alternating serpentinous membersare also radially aligned at their adjacent ends.

Each serpentinous member partially forms an annular array of convolutedaxially extending passageways to provide fluid communication between thecompressor section and the chamber within the combustor.

Compressor air used to cool the combustor walls enters the convolutedpassageways from the compressor, and the air flow throughthesepassageways cools the outer surface of the radially inner wall of thesmooth member of the double wall stepped liner, by convection. Afterflowing through the convoluted passageways, thereby cooling aportion ofthe radially inner double wall step-liner, the air flows along the innersurface of the larger diameter upstream smooth wall member to provide a,cool film of air to thereby insulate the smooth wall from the hotcombustion gases.

The double wall construction enables the cooling air to provide multiplefunctions: (a) to cool each double wallportion of the step-liners byconvective cooling and (b) to cool each double wall portion by providinga cool film or air to insulate the inner wall surface from the hotcombustion gases. A greater cooling effect is achieved when compared topresent temperatures of combustion chambers, or, in the alternativewhere higher combustion chamber temperatures must be handled, theconstruction permits a more efficient utilization of available coolingair to enable operation at the higher temperatures. One US. Patentdisclosing dual/cooling in a combustion chamber is No. 3,545,202.

Further advantages of this combustion chamber construction is thatapproximately the same man-hours are required for constructing thiscombustor relative to prior combustors, and there is substantially, noincrease in the cost associated therewith. A

DESCRIPTION or THE DRAWINGS FIG. 1 is an axial sectional view of aportion of the upper-half of a gas turbine'power plant provided withcombustion apparatus incorporating the invention;

FIG. 2.is an enlarged sectional view of the combustion apparatusillustrated in FIG. 1;

FIG. 3 is a sectional view taken along line III-III in FIG. 2; and

FIG. 4 is a view in perspective of a portion of the combustion apparatusillustrated in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings indetailand especially to FIG. 1, there is shown a portion of a gasturbine power plant having combustion apparatus generally designated 11.However, ,the combustion apparatus may be employed with any suitabletype of gas turbine power plant. The power plant 10 includes an axialflow air compressor 12 for directing air to the combustion apparatus 11and a gas turbine 14 connected to the combustion apparatus 10 andreceiving hot products of combustion therefrom for motivating the powerplant.

Only the upper half of the power plant and combustion apparatus has beenillustrated, since the lower ,half, may be substantially identical andsymmetrical about the centerline or axis of rotation RR of the powerplant.

The air compressor 12 includes, as well known in the art, a multi-stagebladed rotor structure 15 cooperatively associated with a statorstructure having an equal number of multi-stage stationary blades 16 forcompressing the airdirected therethrough to a suitable pressure valuefor combustion in the combustion apparatus 11. The outlet of thecompressor 12 is directed through an annulardiffusion member 17 formingan intake for the plenum'chamber l8, partially defined by a housingstructure 19. The housing 19 includes a shell member of circularcross-section, and as shown of cylindrical shape, parallel with the axisof rotation RR of the power plant 10, a forward dome-shaped wall member21 connected to the external casing of the compressor 12 and a rearwardannular wall member 22 connected to the outer casing of the turbine 14.

The turbine 14, as mentioned above, is of the axial flow type andincludes a plurality of expansion stages formed by a plurality of rowsof stationary blades 24 cooperatively associated with an equal pluralityof rotating blades 25 mounted on the turbine rotor 26. The turbine rotor26 is drivingly connected to the compressor rotor 15 by a tubularconnecting shaft member 27, and a tubular lineror fairing member 28 issuitably supported in' encompassing stationary relation with theconnecting shaft portion 27 to provide a smooth air flow surface for theair entering the plenum chamber 18 from the compressor diffuser l7.

Disposed within the housing 19 are a plurality of tubular elongatedcombustion chambers or combustors 30 of the telescopic step-liner type.The combustion chambers 30 are disposed in an annular mutually spacedarray concentric with the centerline of the power plant and are equallyspaced from each'other in the housing 19. The chambers 30 are arrangedin such a mannerthat their axes are substantially parallel to the outercasing 19 and with the centerline RR of the power plant 10. It ispointed out that this invention is applicable to other types ofcombustors such as the single annular basket type, shown'and describedin the Miller patent, previously cited or the can-annular type havingcomposite features of the canister and annular types.

Since thecornbustors 30 may be substantially identical, only one will bedescribed. As shown in FIG. 1, each combustor 30 is comprised of threesections: an upstream primary portion 32, an intermediate secondaryportion 33 and a downstream transition portion 34.

The forward wall 21 of the combustion apparatus 1 1 is provided with acentral opening 36 through which a fuel injector 37 extends. The fuelinjector 37 is supplied with fuel by a suitable conduit 38 connected toany suitable fuel supply (not shown) and may be of the well knownatomizing type formed in a manner to provide a substantially conicalspray of fuel within the primary portion 32 of the combustion chamber30. A suitable electrical igniter 39 is provided for igniting the fueland air mixture in the combustor 30.

In the primary portion 32 of the combustor 30 are a plurality of linerportions 42 of circularcross-section and in the example shown, the linerportions are cylindrical. The portions 32 are of stepped construction,each of the portions having a circular section of greater circumferenceor diameter than the preceding portion from the upstream to thedownstream end of the combustor to permit telescopic insertion of theportions. Some portions .42 have an annular array of apertures 44 foradmitting primary air from within the plenum chamber 18 into the primaryportion 32 of the combustor to support combustion of fuel injectedtherein by the fuel injector 37. The combustor furtherincludes theintermediate portion 33 which is provided with a plurality of annularrows of apertures 46 for admitting secondary-air from the plenum chamber18 into the combustor 30 during operation, to cool the hot gaseousproducts and make it adaptable to the turbine blades 24'and 25. Thetransition portion 34 is provided with a forward portion 48 ofcylindrical shape disposed in encompassing and slightly overlappingrelation with the intermediate portion 33 as shown by the locking springstructure 47 (FIG. 2). The transition portion 34 is also provided with arearward tubular portion 49 that progressively changes in contour fromcircular crosssection at the jointure with the cylindrical portion 48 toarcuate cross-section at its outlet end portion 50. The arcuate extentofthe outlet 50 is such that, jointly with the outlets of the othercombustors 30, a complete annulus is provided for admitting the hotproducts of combustion from the combustors to the blades 24 and 25 ofthe turbine 14, thereby to provide full peripheral admission of themotivating gases to the turbine 14.

In accordance with the invention, the liner portions 42 of the combustor30 are substantially comprised of a plurality of double walled portions52 (for example five). Each of the portions 52 have a circularcross-section of greater diameter than the preceding portion, from theupstream to the downstream end of the combustor relative to the flow ofair therethrough. The double wall construction of the liner portions 42,as shown, is confined to the primary portion of the combustor 30although it is not limited thereto.

Another way of viewing the double wall portions 52 is that each of theportions includes alternating smooth and corrugated or serpentinous wallmembers 54 and 56, respectively, which overlap each other approximatelyto the center of each respective member. The resulting plurality of thedouble wall portions form the primary portion of the combustor 30.

As best seen in FIGS. 2 and 4, each double wall portion 52 includes analternating smooth wall member 54 and a serpentinous or corrugated wallmember 56. The smooth wall member 54 shown is an elongated tubular orcylindrical member (FIGS. 2 and 3) and each serpentinous member 56 is inthe form of circumferentially corrugated rings comprised of generallytrapezoidal shaped elements 57 (FIG. 3).

Referring to one of the first upstream step-liners 42a, the double wallportion 52 is comprised of an axially extending smooth wall member 54,which forms the radially inner wall of the double wall 52, and a largerdiameter telescoping serpentinous wall member 56 which overlapsapproximately one-half of the smooth wall member 54. Approximatelyone-half of the serpen- .of the half of the serpentinous member 56 whichextends beyond the step 42a in an axial direction. A second largerdiameter smooth wall member 54 overlaps the axially extendingserpentinous wall member 56. The second larger diameter smooth wallmember 54 overlaps approximately one-half of the serpentinous member 56and approximately one-half of the smooth member extends in a downstreamaxial direction. Therefore, the second double wall portion 52 iscomprised of a radially inner wall of a serpentinous member 56 and aradially outer wall of a smooth member 54 to cooperatively form thesecond step liner portion 42 b.

The adjacent downstream end 61 of the first corrugated member 56 and theadjacentupstream end 62 of the second corrugated member 56 aresubstantially aligned in a radial direction relative to the axialcenterline of the combustor 30 and do not overlap in the preferredembodiment. Furthermore, the adjacent downstream end 63 of the firstsmooth member 54 and the adjacent upstream end 64 of the second smoothmember 54 are also substantially radially aligned at their adjacent endsand do not overlap.

The subsequent larger diameter downstream liner portions 42 aresubstantially similar to the first two liner portions 42a and 42bpreviously described. Each liner portion includes an alternating smoothwall member 54 an alternating serpentinous wall member 56 with one partof the serpentinous member overlapping approximately half of the smallerdiameter smooth member and the other half extending in a downstreamaxial direction. In the alternate step, the larger diameter smooth wallmember overlaps approximately one-half of the upstream adjacentserpentinous member to cooperatively form another double wall portion52. In the subsequent step portions 42 the adjacent ends of thealternating smooth members are substantially radially aligned and theadjacent ends of the serpentinous members are also substantiallyradially aligned. I

As best seen in FIGS. 3 and 4, the trapezoidal shaped elements 57 of theserpentinous member 56 have inwardly depressed portions 66, whichcontact the smaller diameter smooth wall member 54, and outwardlydepressed portions 67, which are in spaced relation with the inner wallmember or smooth member 54. In the second step-liner portion 42b (FIG.2) the outwardly projecting portions 67 contact the outer or smooth wallmember 54 and the inwardly depressed portions 66 are in spaced relationtherefrom and form the inner wall of the double wall portion 52.

As best seen in FIG. 4, the serpentinous members 56 are securelyfastened tov the smaller diameter smooth wall member 54 by any suitablemeans 69, preferably by spot welding at a plurality of points ofcontact. The larger diameter smooth wall members 54 are in turn securelyfastened by any suitable means 70, preferably by spot welding at aplurality of points of contact to the smaller diameter serpentinousmember 56 along the outwardly depressed portions 67, which aresubstantially flattened to receive a more rigid spot weld. Only oneannular row of spot welds are used to allow for thermal expansion of themembers 54 and 56 in an axial direction.

The outwardly depressed portions 67 in the serpentinous member 56cooperatively with the smooth wall portion 54 in the first step-linerportion 42a, form a plurality of axial passageways 72 to provide forentry of cooling air indicated by arrow E in FIGS. 2 and 4 from theplenum chamber 18 (FIG. 1) into the combustion chamber 30.

Referring to the second step-liner portion 42b, a second plurality ofaxial passageways 74 are jointly defined by the outer smooth wall member54 and the inwardly depressed portions 66 of the serpentinous member 56.These passageways 74 also provide for entry of cooling air indicated byarrows G from the plenum chamber 18 into the combustion chamber 30.

As previously described, a plurality of apertures 44 are provided withinthe primary portion 32 of the combustor 30. As best shown in FIGS. 2 and4, the apertures 44 are partially formed in both the smooth andserpentinous wall members 54 and 56, respectively. In the preferredembodiment, each aperture 44 is wholly formed in the smooth member 54 asindicated by 44a and partially formed in the serpentinous members 56 asindicated in 44b. Furthermore, each aperture 44 is in registry with oneof the passageways 72, so that a portion of the air from the plenumchamber entering the combustor through aperture 44 is also directedthrough axial passageway 72 for cooling P rposes.

In operation, air is compressed in the compressor 12 (FIG. 1) and flowsinto the plenum chamber 18 within the casing 19. A portion of thepressurized air enters through the primary air apertures 44 where it ismixed with fuel to form a combustible mixture. The hot products ofcombustion then move to the intermediate portion 33 of the combustor 11where secondary air enters the air inlet apertures 46 to cool thegaseous products. The air then is directed through the transitionportion 34 through the outlet.50 to turn the turbine rotor structure 26,the shaft 27 and compressor rotor structure 15.

As previously mentioned under Background Of The Invention, one of themost serious problems with the combustors is to design them to withstandhigh temperatures for extended periods of time. The cooling of thecombustor is as follows. The compressor airfrom the plenum chamber 18(FIG. 1) enters the convoluted axial passageways 72 in a firststep-liner portion 42a because of the pressure drop between the plenumchamber and the combustor. As the air flows through the passageways 72the air convectively cools the inner smooth wall member 54 (or thedownstream half) and also convectively cools the outer serpentinous wallmember 52 (or the upstream half) as indicated by the arrows E in FIG; 2.The air then continues to flow into the second step-liner portion 42b,where it film cools the serpentinous inner wall member 56 (or thedownstream half) and the air continues to flow to the adjacentdownstream portion to provide an insulating film'cooling blanket for thesmooth radially inner wall member 54 (or the downstream half). Thismultiple cooling technique is similar in subsequent step-liner portions42 as indicated by cooling air represented by arrows F enteringconvoluted axially extending passageways 72 and convectively cooling theradially inner smooth 'wall 54, the outer serpentinous vwall member 56and then continuing to provide film cooling for the serpentinous memberand the subsequent downstream smooth wall member 54 of the double wallportions 52.

Additional cooling air represented by arrows G (best seen in FIGS. 2 and4) enters the axially extending passageways 74 in the second step 421:to provide convective cooling for the larger diameter smooth wall member54 and the inner serpentinous member 56 and film cooling for thedownstream smooth wall member 54. This multiple cooling function issimilar in sub sequent step-liner portions.

In large commercial gas turbines, typical testshave indicated thatcombustors burning No. 2 distillate fuel had an average temperature inthe primary portionof approximately 1,600F. Laboratory tests haveindicated using the double wall combustor disclosed herein, that theaverage temperature in the same primary portion were approximately1,000F. under similar testing conditions. This means that the doublewall combustor during actual operating conditions runs at approximately600F. cooler than present combustors which represents a decrease ofabout 36% percent when compared to present combustors.

Furthermore, this reduction in temperature of 600F. is estimated toextend the useful operating life .of the combustors of approximatelyfive times when compared to conventional combustors, while the increasein cost involved in building the double wall combustor relative to theconventional combustor is almost negligible.

As previously mentioned, it is more economical to switch toheavy fuels(those with high hydrocarbon contents and impurities) rather than burnconventional No. 2 distillate fuel. However, since heavy residual fuelsradiate substantially more heat than No. 2 distillate fuel, combustorwalls become hotter and combustor life is correspondingly. substantiallyreduced. Asv

an example, it is not uncommon for combustor wall portions to reach .1,900F. while burning heavy residual fuels. Using the double wallcombustor construction, the wall temperature of the combustors can bekept within present operating temperatures and have useful lives equalto that of conventional combustors.

' Another advantage to the double wall combustor, is that no additionalcooling air is needed to cool the walls and the temperature distributionpattern of the gases introduced to the turbine blades arenot effectedthereby. Alternately, to maintain the same temperature of the combustorwalls, the amount of compressorair could be substantially reducedthereby increasing the overall efficiency of the turbine because of thereduction in back work.

' An additional advantage of the double wall combustor is thatsince thecombustor walls are cooler, the pressurized air within the plenumchamber is also kept cooler resulting in a cooler outer casingstructure.

What is disclosed then, is a double wall combustor that'providesmultiple cooling functions: (a) convec tively cools each double wallportion, and (b) film cools each double. wall portion. The double wallcombustor runs substantially cooler when compared to presenttemperatures of combustors or in the alternative can operate atsubstantially higher temperatures without having a correspondingdecrease in combustor life. When operated at normal conditions, thecombustor has an increase of useful life of five times that of presentcombustors, with substantially no increase in construction costassociated therewith. Finally, the temperature distribution pattern ofthe hot combustion gases are not affected by the double wallconstruction.

Since numerous changes may be made in the abovedescribed construction,and different embodiments of the invention may be made without departingfrom the spirit and .scope thereof, it is intended that all the mattercontained in the foregoing description or shown in the accompanyingdrawings, shall be interpreted as illustrative and not in a limitingsense.

We claim as our invention:

1; In a combustion chamber arranged for admission of fuel to theupstream end thereof and discharge of hot gaseous products from thedownstream end thereof, an elongated tubular wall structure of astep-liner construction incrementally increasing in cross sectional areain downstream direction and having a double wall, said double wallcomprising, serpentinous wall members and smooth wall members, saidsmooth wall members being disposed adjacent each other in such a mannerthat upstream smooth wall members are circumferentially smaller thanadjacent downstream smooth wall members and a serpentinous wall memberoverlaps adjacent smooth wall members to form said tubular double wallstructure, said serpentinous and smooth wall members being so disposedthat an upstream portion of each of said serpentinous members enwrapsand fastens to a downstream portion of a smooth wall member andtelescopes within and fastens to an upstream portion of an adjacentsmooth wall member, whereby said combustion chamber has a double wallthroughout said elongated tubular step liner structure.

2. The structure recited in claim 1, wherein the adjacent smooth membershave ends which are substantially radially aligned.

3. The structure recited in claim 1, wherein the serpentinous membershave ends which are substantially radially aligned.

4. The structure recited in claim 1, wherein the serpentinous wallmembers partially define an array of first passageways, generallyextending in the axial direction, to permit cooling fluid toconvectively cool the enwrapped smooth wall member and gaseous productswithin the combustion chamber and the adjacent downstream smooth wallmembers.

5. The structure recited in claim 4, wherein the cooling fluid alsoconvectively cools the portion of the serpentinous wall membersenwrapping the downstream portion of the smooth wall members.

6. The structure recited in claim 4, wherein the cooling fluid furtherfilm cools the adjacent serpentinous wall members telescoping in theupstream portion of the smooth wall members.

7. The structure recited in claim 4, wherein the serpentinous wallmembers partially define an array of second passageways generallyextending in the axial direction to permit cooling fluid to convectivelycool the serpentinous wall members and the enwrapped smooth wall member,and furthermore to allow cooling fluid to provide a cooling film offluid adjacent the downstream portion of the smooth wall members.

8. The structure recited in claim 1 wherein there is no substantialoverlap between adjacent smooth wall members.

9. The structure recited in claim 1 wherein there is no substantialoverlap between adjacent serpentinous wall members.

10. The structure recited in claim 1, having a primary combustion zoneadjacent the downstream end thereof.

11. The structure recited in claim 10, and further comprising an arrayof primary air inlet apertures disposed in the primary combustion zone.

12. The structure recited in claim 1 and further comprising an array ofapertures disposed adjacent the upstream end of the combustion chamberfor admitting air thereto, said apparatus being formed jointly in thesmooth and serpentinous member.

13. The structure recited in claim 12, wherein each of the apertures iswholly formed in a smooth wall member and partially formed in adjacentserpentinous wall members.

14. The structure recited in claim 1, wherein the serpentinous wallmembers are tubular and are comprised of elements having a substantiallytrapezoidal shaped cross-section.

casing structure at least partially defining a pressurized plenumchamber,

a plurality of combustion chambers disposed in an annular array withinsaid casing structure, the centers of said chambers being equidistantfrom each other in an annular direction each of said combustion chambershaving a tubular double wall structure of step-liner construction,incrementally increasing in cross sectional area in downstreamdirection,

said double wall structure comprising serpentine wall members and smoothwall members,

said smooth wall members being disposed adjacent each other in such amanner that upstream smooth wall members are circumferentially smallerthan adjacent downstream smooth wall members and a serpentinous wallmember overlaps adjacent smooth wall members to form said tubular doublewall structure, said serpentinous and smooth wall members being sodisposed that an upstream portion of each of said serpentinous membersenwraps and fastens to a downstream portion of a smooth wall member andtelescopes within and fastens to an upstream portion of an adjacentsmooth wall member, whereby said combustion chamber has a double wallthroughout said tubular step liner structure.

17. The structure recited in claim 16, wherein the adjacent smoothmembers have ends which are substantially radially aligned.

18. The structure recited in claim 16, wherein the serpentinous membershave ends which are sub stantially radially aligned.

19. The structure recited in claim 16, wherein the serpentinous wallmembers partially defines a first array of passageways extendinggenerally in an axial direction to provide fluid communication betweenthe plenum chamber and the combustion chamber,

said first passageways permitting cooling fluid to convectively cool theenwrapped smooth wall member and the enwrapping serpentinous member,

and said passageways being arranged to permit said cooling fluid toprovide a fluid film between hot combustion gases within the combustionchamber and the adjacent serpentinous wall members telescoped within thesmooth wall member and to produce a fluid film between the hotcombustion gases and the enwrapped smooth wall members.

20. The structure recited in claim 19, wherein the serpentinous wallmembers partially defines a second array of passageways extendinggenerally in an axial direction,

said passageways permitting cooling fluid to convectively cool theserpentinous wall members and telescoped with the smooth wall members,

and furthermore, to allow the cooling fluid to provide a film of coolingfluid adjacent the enwrapped smooth wall members.

1. In a combustion chamber arranged for admission of fuel to theupstream end thereof and discharge of hot gaseous products from thedownstream end thereof, an elongated tubular wall structure of astep-liner construction incrementally increasing in cross sectional areain downstream direction and having a double wall, said double wallcomprising, serpentinous wall members and smooth wall members, saidsmooth wall members being disposed adjacent each other in such a mannerthat upstream smooth wall members are circumferentially smaller thanadjacent downstream smooth wall members and a serpentinous wall memberoverlaps adjacent smooth wall members to form said tubular double wallstructure, said serpentinous and smooth wall members being so disposedthat an upstream portion of each of said serpentinous members enwrapsand fastens to a downstream portion of a smooth wall member andtelescopes within and fastens to an Upstream portion of an adjacentsmooth wall member, whereby said combustion chamber has a double wallthroughout said elongated tubular step liner structure.
 2. The structurerecited in claim 1, wherein the adjacent smooth members have ends whichare substantially radially aligned.
 3. The structure recited in claim 1,wherein the serpentinous members have ends which are substantiallyradially aligned.
 4. The structure recited in claim 1, wherein theserpentinous wall members partially define an array of firstpassageways, generally extending in the axial direction, to permitcooling fluid to convectively cool the enwrapped smooth wall member andgaseous products within the combustion chamber and the adjacentdownstream smooth wall members.
 5. The structure recited in claim 4,wherein the cooling fluid also convectively cools the portion of theserpentinous wall members enwrapping the downstream portion of thesmooth wall members.
 6. The structure recited in claim 4, wherein thecooling fluid further film cools the adjacent serpentinous wall memberstelescoping in the upstream portion of the smooth wall members.
 7. Thestructure recited in claim 4, wherein the serpentinous wall memberspartially define an array of second passageways generally extending inthe axial direction to permit cooling fluid to convectively cool theserpentinous wall members and the enwrapped smooth wall member, andfurthermore to allow cooling fluid to provide a cooling film of fluidadjacent the downstream portion of the smooth wall members.
 8. Thestructure recited in claim 1 wherein there is no substantial overlapbetween adjacent smooth wall members.
 9. The structure recited in claim1 wherein there is no substantial overlap between adjacent serpentinouswall members.
 10. The structure recited in claim 1, having a primarycombustion zone adjacent the downstream end thereof.
 11. The structurerecited in claim 10, and further comprising an array of primary airinlet apertures disposed in the primary combustion zone.
 12. Thestructure recited in claim 1 and further comprising an array ofapertures disposed adjacent the upstream end of the combustion chamberfor admitting air thereto, said apparatus being formed jointly in thesmooth and serpentinous member.
 13. The structure recited in claim 12,wherein each of the apertures is wholly formed in a smooth wall memberand partially formed in adjacent serpentinous wall members.
 14. Thestructure recited in claim 1, wherein the serpentinous wall members aretubular and are comprised of elements having a substantially trapezoidalshaped cross-section.
 15. The structure recited in claim 14, wherein thetrapezoidal shaped elements jointly define inwardly and outwardlydepressed portions the outer surfaces of which contacts the adjacentsmooth wall members.
 16. In a gas turbine power plant comprisingcombustion apparatus having an outer casing structure, said casingstructure at least partially defining a pressurized plenum chamber, aplurality of combustion chambers disposed in an annular array withinsaid casing structure, the centers of said chambers being equidistantfrom each other in an annular direction, each of said combustionchambers having a tubular double wall structure of step-linerconstruction, incrementally increasing in cross sectional area indownstream direction, said double wall structure comprising serpentinewall members and smooth wall members, said smooth wall members beingdisposed adjacent each other in such a manner that upstream smooth wallmembers are circumferentially smaller than adjacent downstream smoothwall members and a serpentinous wall member overlaps adjacent smoothwall members to form said tubular double wall structure, saidserpentinous and smooth wall members being so disposed that an upstreamportion of each of said serpentinous members enwraps and fastens to adownstream portion of a smooth wall member and telescopes within andfastens to an upstream poRtion of an adjacent smooth wall member,whereby said combustion chamber has a double wall throughout saidtubular step liner structure.
 17. The structure recited in claim 16,wherein the adjacent smooth members have ends which are substantiallyradially aligned.
 18. The structure recited in claim 16, wherein theserpentinous members have ends which are substantially radially aligned.19. The structure recited in claim 16, wherein the serpentinous wallmembers partially defines a first array of passageways extendinggenerally in an axial direction to provide fluid communication betweenthe plenum chamber and the combustion chamber, said first passagewayspermitting cooling fluid to convectively cool the enwrapped smooth wallmember and the enwrapping serpentinous member, and said passagewaysbeing arranged to permit said cooling fluid to provide a fluid filmbetween hot combustion gases within the combustion chamber and theadjacent serpentinous wall members telescoped within the smooth wallmember and to produce a fluid film between the hot combustion gases andthe enwrapped smooth wall members.
 20. The structure recited in claim19, wherein the serpentinous wall members partially defines a secondarray of passageways extending generally in an axial direction, saidpassageways permitting cooling fluid to convectively cool theserpentinous wall members and telescoped with the smooth wall members,and furthermore, to allow the cooling fluid to provide a film of coolingfluid adjacent the enwrapped smooth wall members.